The present disclosure relates to a method and an assembly for guidance of an aircraft during a low-altitude flight.
In a standard manner, a low-altitude flight phase, called LLF (“Low Level Flight”) phase, allows an aircraft to fly at low altitude, in particular so as to follow as closely as possible the terrain overflown, especially so as to avoid being pinpointed, while removing any risk of collision with a part of the terrain. Such an LLF phase generally takes place at a predetermined terrain altitude, for example at 500 feet (about 150 meters).
In particular, for a military aircraft, especially a military transport airplane, one of the objectives of a low-altitude flight is to exploit the masking in relation to the terrain to protect oneself from threats in hostile geographical zones. Accordingly, in particular in order to carry out in-flight instrument based operations of IMC (“Instrument Meteorological Conditions”) type, a flight management system of FMS (“Flight Management System”) type computes in a standard manner a three-dimensional reference trajectory (taking into account the terrain overflown), and the aircraft is guided along this reference trajectory (either automatically with the aid of an automatic piloting system, or manually by following indications presented by a flight director).
The aircraft's flight management system is therefore responsible for the computation of the reference trajectory. This reference trajectory is computed using data relating to the terrain overflown and the aircraft's climb and descent capabilities, as well as its maneuvering capabilities.
Furthermore, the aircraft comprises a guidance system comprising at least one guidance computer, of FGC (“Flight Guidance Computer”) type, which is responsible for slaving the aircraft to this reference trajectory.
A flight of IMC LLF type being subject to safety rules, the flight management and guidance systems must, inter alia, ensure that a minimum trajectory distance (called the MEMO distance) is available and validated ahead of the aircraft during guidance (or before guidance, so as to authorize guidance). Consequently, the flight trajectory that the aircraft has to follow must be transmitted in advance by the flight management system. The guidance system makes sure of the storage and validation of this trajectory.
Furthermore, a trajectory constructed by the flight management system, and such as defined in a flight plan, may be revised or canceled. In the case of such a revision before the flight of an LLF phase, the former trajectory is removed from the flight management system. It is in particular necessary that the guidance system not slave the aircraft to a trajectory (previously received and stored) that is unknown to the flight management system.
Furthermore, the architecture and the operation of these two systems (flight management system and guidance system) must ensure that the aircraft can only be guided on a valid trajectory (meeting the safety criteria) that the pilot knows (via the flight management system) and desires be flown, and that the low-altitude flight capability is not lost upon a change of trajectory.